This type of upright wheelchair is known for example from EP 0 815 822 B1.
The seated posture of a wheelchair occupant maintained over a long period results in physical breakdown of bodily functions, such as for example reduced mobility of the lower limbs, a slowdown in bowel activity and impairment to blood circulation. Sitting also adds the risk of bedsores. An upright wheelchair aids in reducing these consequences, since the breakdown of bodily functions is reduced by changing posture, including standing. The pivoting seat area is mounted with back and footrest on a chassis. Correct adapting to the anatomical requirements of the user is a vital criterion for comfort offered by the wheelchair.
Upright wheelchairs also offer the user the option of taking part in sports, such as playing golf. In such a case it is particularly important that the wheelchair offers a high degree of standing stability in the upright position. It is a requirement for example for the footrest to stand on the ground or respectively to be supported thereon when the wheelchair is in the upright position. The seat back must be parallel to the seat area and the golfer must be given adequate opportunity for movement (turning of the upper body) to be able to swing properly.
When the seat is switched to the standing position the footrest is lowered in the direction of the ground. By altering the height of the foot support relative to the ground the distance between seat area and footrest is also changed at the same time. This is necessary, since the anatomical axis of rotation in the knee joint does not coincide with the axis of rotation of the seat area. For the wheelchair to be secure in the standing position the footrest plane must be lying on the ground, therefore aligned substantially perpendicularly to the chassis. A comfortable seating position is assumed by way of contrast whenever the foot assembly (or respectively the foot stand area) is inclined in relation to the horizontal, therefore does not run parallel to the ground. Since standing security has a higher priority than seating comfort in the case of the known wheelchair the footrest also is not inclined in the seating position, rather it runs parallel to the ground. The patient consequently assumes an anatomically inappropriate seating posture; with a greater knee angle the patient sustains deformity of the foot.